Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone.
Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto.
One type of joint replacement surgery is shoulder arthroplasty. During shoulder arthroplasty, the humeral head must be resected to allow for the insertion of a humeral stem into the intramedullary canal of the humerus. The proximal end of the humerus includes the humeral head, which articulates with the glenoid of the shoulder in a ball and socket fashion. The humeral head is nearly hemispherical in form.
The prostheses typically used for shoulder arthroplasty include a stem portion designed to extend into the intramedullary canal of the humerus and a head portion designed to replace the humeral head. The head portion of the prosthesis extends angularly from the stem portion. The resection of the natural humeral head must be made so that the angle of the cut corresponds to the angle between the stem and head portions of the prosthesis. In addition, the rotation of the cut varies to adjust to bone wear or capsular looseness.
Patients who have massive rotator cuff tears experience proximal migration of the humerus. When this occurs, part of the humeral head will contact the acromion, which can cause pain and loss of shoulder function. By providing a humeral head with an extended articulating surface, a metal surface with a low coefficient of friction will contact the acromion and reduce pain. The extended articulating surface also increases the surface of articulation in the artificial shoulder joint in abduction and external rotation.
When implanting a proximal humeral resurfacing implant with an extended articulation surface, removal of part or all of the humeral greater tubercle is needed. After the initial humeral head resection is made, a portion of the greater tubercle must also be removed. The cut that achieves this is perpendicular to the longitudinal axis of the humerus and allows for the backside of the extended articulation surface to sit on the most superior portion of the humerus.
One surgical technique used in shoulder arthroplasty is called the deltopectoral approach. This approach requires detachment of the anterior portion of the rotator cuff from the humerus in order to gain adequate exposure to the joint. This is not ideal for the patient because the disturbance of the anterior cuff can compromise the function of the shoulder.
A second technique used in shoulder arthroplasty is the anterosuperior approach. Unlike the deltopectoral approach, the anterosuperior approach spares the anterior portion of the rotator cuff. However, it requires disturbance of other soft tissue structures, namely the origin of the anterior deltoid and the acromial insertion of the coracoacromial ligament, which can also compromise shoulder function.
Clearly, neither of these approaches is ideal for the patient. What would be ideal is a third technique that spares the anterior rotator cuff, the origin of the anterior deltoid, and the insertion of the coracoacromial ligament. A soft tissue approach of this type has been identified, but there is not adequate instrumentation to guide the resection of the greater tubercle of the humerus from this approach. The soft tissue approach provides exposure to the humerus from the lateral side. Therefore, an instrument that aids the resection of the greater tubercle of the humerus from the lateral direction is needed.